Max Weight of Non Lift Producing Components

We weighed everything together and then the wings. Felt that was easier than trying to hold the fuselage with tail attached upright and on the scales.

So what does the main pin(s) count as?

KN

At 16:07 30 November 2017, Tony wrote:
We weighed everything together and then the wings. Felt that was easier
than trying to hold the fuselage with tail attached upright and on the
scales.

On 11/30/2017 9:53 AM, Kevin Neave wrote:
So what does the main pin(s) count as?

KN

At 16:07 30 November 2017, Tony wrote:
We weighed everything together and then the wings. Felt that was easier
than trying to hold the fuselage with tail attached upright and on the
scales.

Try flying without it/them in place and get back to the group how it went!

More seriously, and structurally, it/they are part(s) of the wing.

Bob W.

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This email has been checked for viruses by AVG.
http://www.avg.com

Part of the wings, yes, but certainly not lift generating.Â* But you
can't do without them...

On 11/30/2017 10:15 AM, BobW wrote:
On 11/30/2017 9:53 AM, Kevin Neave wrote:
So what does the main pin(s) count as?

KN

At 16:07 30 November 2017, Tony wrote:
We weighed everything together and then the wings. Felt that was
easier than trying to hold the fuselage with tail attached upright
and on the scales.

Try flying without it/them in place and get back to the group how it
went!

More seriously, and structurally, it/they are part(s) of the wing.

Bob W.

---
This email has been checked for viruses by AVG.
http://www.avg.com


--
Dan, 5J

BGA has a concession which allows for non-aerobatic flights to exceed the maximum weight of non-lifting parts by 3%, so my that margin it should be fine.

Does anyone know, how exceeding that non-lifting weight influences the flutter of the wing?

Stefan

No, it doesn't influence flutter. Flutter is controlled by the eigenfrequencies of the wing.

On Thu, 30 Nov 2017 10:07:57 -0800, phouchg278 wrote:

Does anyone know, how exceeding that non-lifting weight influences the
flutter of the wing?

Its more a structural thing than load related.

Increasing surface torsional stiffness delays the onset of flutter and
putting the CG of the flying surface in front of the torsion axis damps
it out.


--
Martin | martin at
Gregorie | gregorie
| dot org

On Friday, December 1, 2017 at 3:44:44 AM UTC-8, Kiwi User wrote:
On Thu, 30 Nov 2017 10:07:57 -0800, phouchg278 wrote:

Does anyone know, how exceeding that non-lifting weight influences the
flutter of the wing?

Its more a structural thing than load related.


For the non engineers that might read this..... a loading illustration
using two examples:

Use a (really long)tongue depressor and white glue to glue a hollowed out eggshell to the half span point. Let it dry. Take a wing tip and do anything you like to shake the egg off the stick. Not enough mass in the eggshell to part it from the stick. Safe scenario = under max non-lifting parts weight.

The worst case scenario is the same eggshell full of heavy stuff. Mercury would be great - but its impractical. Imagine it. Load that egg (fiberglass shell) to the max, and then introduce a bunch of G's via centrifical or gust(rotor flight)force. The eggshell will rip off the stick(spar). Or, the stuff inside the shell will rupture it and leave the scene - think an over-max-payload person attached to max 242 lb. (110 kg) seat belt attaching points.

There are recurring discussions about how much margin designers provide for protection from this and that (max non lifting, Vne, gust loads, seatpan loads). My response is always - do you know the life history of this pretty fiberglass? The controlrod end play? The hingepoint tightness? How many times someone flew it how close to/over Vne due to an antique instrument or partially plugged pitot line? I am not in favor of flying beyond manufacturer's limits for anything.....
thanks for the many contributors to good info on this thread.

Cindy B

On Friday, December 1, 2017 at 10:00:14 AM UTC-8, CindyB wrote:

There are recurring discussions about how much margin
designers provide for protection from this and that...

One of the more high-profile examples is this RV-10 airplane for which the amateur builder arbitrarily increased the gross weight by a hundred pounds. Designer Dick Vangrunsven rightfully took issue with this practice:

https://www.facebook.com/notes/vans-...37594966250883

...I am not in favor of flying beyond manufacturer's limits for anything...

That's the best plan!

--Bob K.

On Thursday, November 30, 2017 at 9:00:07 AM UTC-8, Kevin Neave wrote:

So what does the main pin(s) count as?

Very incisive question! That's a good demonstration of how the mass of non-lifting is a reasonable metric for the approximation of wing main spar maximum bending moment, but is still just an approximation.

At issue is that using a maximum mass of non-lifting parts to limit the wing spar bending moment is only valid when any mass added to the wings is distributed spanwise according to the wing lift distribution. So if for whatever reason you add a bunch of mass to the inboard ends of the wings (depleted uranium root ribs maybe?), you can be within the allowable non-lifting mass and within the load factor envelope, but still develop excessive wing spar bending moment.

Bottom line: Respect mass limits to the spirit and the letter of the published values. And if you want a glider with lots of non-lifting mass margin, build an HP-24. The one we finished last summer has an empty non-lifting mass of ~220 lbs (ready to fly with batteries, instruments, 24 ft^2 O2 bottle, etc) and a maximum of ~605 lbs, yielding a payload of ~385 lbs for pilot, parachute, FES, electric self-launch, BRS, etc.

--Bob K.